The Missouri death row prisoner Reggie Clemons will make one final appeal on Monday at a special hearing that marks the last glimmer of hope that his life might be spared.

Clemons and his defence lawyer, alongside the opposing legal team of the state of Missouri, will come before judge Michael Manners in his court room in Independence, Missouri, to give their final oral arguments in what amounts to one last role of the dice for Clemons. The prisoner has been on death row for 20 years for the double murder of two sisters who were raped and thrown off the Chain of Rocks bridge over the Mississippi in April 1991.

Clemons, 41, has consistently claimed innocence. In the course of a three-hour interview with the Guardian, filmed in prison, he said: "I know, and God knows I'm not a rapist. I know I'm not a murderer or a killer. I know I didn't do any of these things. I know I'm innocent."

At Monday's final hearing, the onus will be on Clemons as the petitioner to persuade the judge that as a result of new evidence that has come to light since his 1993 trial his death sentence is no longer sound. Once he has heard both sides of the argument, Manners will prepare his own conclusions in the case and make recommendations to the Missouri supreme court on what should happen to Clemons – should he be granted a new trial, should his sentence be commuted to life in prison with no chance of parole, or should he be sent back to death row in which case his execution would almost certainly go ahead.

In final written arguments prepared for the judge, Clemons's lawyer, New York attorney Joshua Levine, has concentrated on three peculiarities of the case that he argues should lead to a retrial, or at least commutation to a life sentence. First, the defence has presented new evidence that an all-important "confession" that Clemons made to police shortly after the Kerry sisters fell to their deaths in April 1991 was beaten out of him.

In the "confession", Clemons admitted to raping one of the women and having participated in the events that led to them being pushed into the river. In 1993, the prosecutor referred to the evidence more than 10 times during his summing up to the jury at trial.

Yet Clemons retracted the statement the day after he made it, complaining it had been forced from him through police brutality. Since the previous hearing in front of Manners last September, new testimony has been deposed that has never been heard before from a bail investigator called Warren Weeks who interviewed Clemons just a few hours after his police questioning.

Weeks swore under oath that he had seen a "golf-ball-sized welt" and "a rather large bump on the side of his face" that he had interpreted to be a result of the interrogation. Weeks also testified that he recalled writing "bump" or "bruise" on an official form at the time of his interview with Clemons in April 1991.

Yet, Weeks said, those words appeared to have been scratched out from the form by someone other than himself. Weeks went on to recall that a few weeks after he had seen Clemons he was called in to talk to the chief prosecutor in the case, Nels Moss – a request that he thought highly unusual. Weeks said he had felt "pressure not to say anything about the injury he had seen".

Clemons's defence team argues that this was just one element of vital evidence that was suppressed before the trial in a way that violated his constitutional right to a fair hearing. Another crucial factor, Levine argued at last September's special hearing, was that the defendant was not told before trial that edited changes were made to a draft police report relating to the events of the night of the sisters' death. The edits had been made at the request of the prosecutor, Moss.

Under intense questioning from Levine, Moss admitted at the September hearing that he had marked up the draft police report, and made several important changes to it, because he thought it was "inaccurate".

For its part, the prosecution team is likely to argue before Manners that Clemons's petition falls short on all its major points and that the prisoner should be returned to death row to face execution. In its final written arguments, the state of Missouri argues that there is nothing substantively new in Clemons's claims sufficient to negate the verdict of the original jury.

"Merely putting a different spin on evidence that was presented to the jury does not satisfy" the legal requirements for a retrial or commutation, the document says. The prosecution remind the judge that in the September hearing Clemons refused to answer a succession of probing questions about what happened on the Chain of Rocks bridge that night, claiming the Fifth Amendment right against self-incrimination.

Before Clemons pleaded the fifth to 29 questions, the judge had warned him that he did not have any constitutional protection because this was a civil hearing and not a trial, and that his silence would be interpreted negatively. "Clemons has not shown that he is probably actually innocent," the prosecution argue.

The prosecution also draw on results of DNA testing from a condom found on the bridge and from clothes warn by co-defendants. Though the results are not conclusive, Clemons's DNA profile could not be eliminated from some of the findings.

Four young men were arrested and charged with the murders of Julie and Robin Kerry: Clemons, then 19; Marlin Gray who was executed in 2005; Antonio Richardson who is serving a life sentence; and Daniel Winfrey. The state did a deal with Winfrey, the only white man among the four, and he turned witness for the prosecution; he was released on parole in 2007.

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